Re: 9mm Carbines ?
The "Just Right" setups are "JUST WRONG!" (As are most things from ATI...the EMF is the same old whore in a different dress).
They are generally poor performers, unreliable, suffer from poor accuracy, and good luck getting parts and aftermarket support for them. The nice thing is that they do use cheap and plentiful Glock mags, but that's where the good news ends!
As for AR's in 9mm...I've got extensive experience with everything from the original Colts (and the current ones too) to custom built uppers and complete rifles. To address some of your questions/concerns.
The RRA 9mm carbines now all have the RRA proprietary lower which is forged with the magwell for the 9mm mags already integral to the lower. No need for 9mm magwell adapters, but that also prohibits you from switching calibers to .223/5.56 or the host of other calibers supported by the standard AR-15 lower. This is true for all the 9mm RRAs made in the last several years, but RRA also used to make 9mm-marked AR lowers with the magwell adapters too which you may also find for sale. I only point this out because that difference matters to some. That said, the RRA 9mm carbines I have run perform very well with a wide variety of ammo. I personally ONLY use the OEM Colt/Metalform 9mm AR mags in any of my guns and recommend the same to others as the uzi conversion mags can sometimes have issues and the 9mm Promags are just as terrible as their other mags. The C-Products 9mm AR mags were generally hit/miss in terms of function/reliability.
Also consider:
1) Spike's Tactical can build you the 9mm upper of your dreams based on your specs;
2) CMMG makes a very nice 9mm upper (as well as 9mm conversion parts, including the highly desired ramped 9mm bolt/carrier assembly which allows you to use standard AR-15 hammers instead of the dedicated, one-off 9mm hammer (saves you from having to worry about yet one more non-standard part to carry/replace if something breaks...Spike's, YHM and other highly regarded mfgs use the CMMG 9mm bolt setups);
3) finally, Yankee Hill Machine Co (YHM) also makes some nice, albeit somewhat pricey, 9mm uppers.